Particle size independent spectrometric determination of wear metals in aircraft lubricating oils

A method for the particle size independent determination of Ni, Fe, Mg, Cu, Al, Sn, Mo and Ti in synthetic ester lubricating oils by spectrometric analysis is presented. Partial dissolution of Cr, Si, Pb and Ag also occurs. Used ester lubricating oils and samples prepared with -- 325 mesh (44 mu m) or -- 200 mesh (74 mu m) metal powders were reacted with a small amount of hydrofluoric acid and aqua regla at 65 deg C for 45 min with ultrasonic agitation. The reacted mixture was then diluted with a methyl isobutyl ketone and isopropyl alcohol mixture and analyzed spectrometrically. The recoveries for metal powder suspensions of Ni, Fe, Mg, Cu, Al, Sn, Mo and Ti ranged from 97 to 103% and the relative standard deviation ranged from 4 to 10%. In addition to the metal powder suspensions, > 200 aircraft oil samples were analyzed. The method is much faster and more convenient than previously reported particle size independent methods using ashing techniques.19 refs.--AA